Current roll-to-roll soft lithography processes for embossing a photopolymer coated web include a process and apparatus used by Epigem Ltd., wherein a web material that is transparent to ultraviolet light is coated with a layer of photopolymer resist and the coated side of the web is brought into contact with an embossing shim that carries an imprint pattern. When the web separates from the embossing shim, the imprint pattern is embossed in (i.e. is replicated in) the layer of photopolymer resist. An ultraviolet light source irradiates the layer of photopolymer resist through the web and cures the embossed pattern so that the pattern hardens and retains its embossed shape. Because the web is transparent to the ultraviolet light, placement of the ultraviolet light source is not problematic and the embossing shim can be opaque to ultraviolet light and the irradiation can occur from the web side.
One disadvantage of the above apparatus is that if the web material and the embossing shim are opaque to ultraviolet light, then the irradiation will not be effective from the web side or the embossing shim side. Accordingly, if a roll-to-roll process requires the web material to be opaque to ultraviolet light, then the embossing shim must be optically transparent to the ultraviolet light so that the irradiation of the embossed pattern in the layer of photopolymer resist can occur from the embossing shim side.
In contrast, researchers at various universities (e.g. University of Texas at Austin, Step and Flash Imprint Lithography) have used quartz shims (templates) that are optically transparent to ultraviolet light. However, that process is a batch oriented wafer-based process that is not suitable for a roll-to-roll soft lithography process.
Consequently, there is an unmet need for an apparatus for implementing a roll-to-roll soft lithography process wherein an optically transparent compliant media that carries an imprint stamp, is used to emboss a pattern in a photopolymer coated on an opaque flexible substrate. There is also a need for an apparatus that allows the pattern embossed in the flexible substrate to be cured by ultraviolet light that irradiates the pattern through the compliant media and the imprint stamp.